Term: absolute full energy peak efficiency https://doi.org/10.1351/goldbook.A00023 Definition: Of a radiation spectrometer, the counting efficiency when considering only the events recorded in the full energy peak. Related Terms: 1) radiation (http://doi.org/10.1351/goldbook.R05048). 2) counting efficiency (http://doi.org/10.1351/goldbook.C01377). 3) full energy peak (http://doi.org/10.1351/goldbook.F02546). 4) spectrometer (http://doi.org/10.1351/goldbook.S05837). Source: PAC, 1982, 54, 1533. 'Glossary of terms used in nuclear analytical chemistry (Provisional)' on page 1543 (https://doi.org/10.1351/pac198254081533) Citation: 'absolute full energy peak efficiency' in IUPAC Compendium of Chemical Terminology, 5th ed. International Union of Pure and Applied Chemistry; 2025. Online version 5.0.0, 2025. https://doi.org/10.1351/goldbook.A00023 License: The IUPAC Gold Book is licensed under Creative Commons Attribution-ShareAlike CC BY-SA 4.0 International (https://creativecommons.org/licenses/by-sa/4.0/) for individual terms. Disclaimer: The International Union of Pure and Applied Chemistry (IUPAC) is continuously reviewing and, where needed, updating terms in the Compendium of Chemical Terminology (the IUPAC Gold Book). Users of these terms are encouraged to include the version of a term with its use and to check regularly for updates to term definitions that you are using.